President Barack Obama has been under pressure in recent weeks. Photograph: Alex Wong/Getty Images

Barack Obama's hopes of moving beyond the scandals that have dogged his administration were dashed on Monday, when it was disclosed that the White House had been informed last month about the details of the IRS affair.

But the Wall Street Journal on Monday picked up an important discrepancies in the official White House versions of how much it knew about the IRS scandal in advance.

Obama has said that he learned about the scandal at the same time as the press, on 10 May. Last Monday Obama's press spokesman, Jay Carney, said that the White House counsel Kathryn Ruemmler had been informed in April that an independent audit of the scandal had been completed, but had not been given the findings. A White House adviser, Dan Pfeiffer, interviewed on CBS on Sunday, echoed Carney's line, saying the White House had been made aware of the scandal a few weeks ago by the Treasury, although not the full details of what had happened.

But the WSJ reported that Ruemmler learned from Treasury lawyers on 22 April that "a small number of line IRS employees had improperly scrutinised certain … organizations by using words like 'tea party' and 'patriot'".

Republicans, who have been trying to establish a link between the IRS scandal and the White House, seized on the apparently contradictory statements. "I just don't know who I can believe anymore," said Brendan Buck, spokesman for the Republican House Speaker, John Boehner.

The scandal involves an IRS office in Cincinnati, Ohio, which selected for extra scrutiny conservative groups with words such as 'tea party' or 'patriot' in their titles. The IRS denies this was for partisan reasons but admitted applications by these groups for tax-exempt status have been delayed.

In another sign that the scandals will not die away quickly, Tea Party groups are to launch a lawsuit against the IRS for discriminating against them. Another came in a letter sent to the IRS on Monday by the Senate finance committee.

The committee chairman Max Baucus, a Democrat, and Orrin Hatch, the ranking Republican, list a series of demands for internal documents relating to the scandal and the names and position of everyone who had been either involved in or informed about it. The deadline for the hand-over of the material is 31 May.

A House hearing began on Friday but the Senate enjoys a lot more power. In their joint letter, Baucus and Hatch wrote: "Targeting applicants for tax-exempt status using political labels threatens to undermine the public's trust in the IRS. The lack of candor in advising the Senate of this practice is equally troubling."

In a separate development, the Washington Post on Monday disclosed new details of the Obama administration's crackdown on leaks to journalists.

Court documents obtained by the Post showed that the Department of Justice tracked the comings and goings to the State Department of James Rosen, the chief Washington correspondent of Fox News.

Officials wanted to track his connections with Stephen Jin-Woo Kim, a former state department adviser, in relation to alleged leaks of classified information about North Korea in 2009. By using Rosen's security badge access, Justice officials were able to track the timings of his visits to the State Department. They also seized Rosen's phone records and personal emails. Kim was indicted by a grand jury in August 2010, over an alleged conversation with Rosen about a North Korea nuclear bomb test.

The Department of Justice's seizure of AP phone records in relation to a leak of a CIA operation to stop a bomb plot hatched in Yemen has not yet had the same traction as the IRS scandal. But the involvement of a Fox News reporter excited rightwing commentators on Monday.

The Obama administration has launched more actions against whistleblowers than any previous presidency, prompting accusations that it has launched a "war on journalism".